Nonlinear Optical Material and Methods of Fabrication

ABSTRACT

Disclosed is a nonlinear optical (NLO) material for use in deep-UV applications, and methods of fabrication thereof. The NLO is fabricated from a plurality of components according to the formula A q B y C z  and a crystallographic non-centrosymmetric (NCS) structure. The NLO material may be fabricated as a polycrystalline or a single crystal material. In an embodiment, the material may be according to a formula Ba 3 ZnB 5 PO 14 .

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of Ser. No. 16/120,366,filed Sep. 3, 2018, and entitled “Nonlinear Optical Material and Methodsof Fabrication”, which is a divisional application of U.S. patentapplication Ser. No. 15/563,903 (now U.S. Pat. No. 10,133,148), filedOct. 2, 2017, and entitled “Nonlinear Optical Material and Methods ofFabrication”, which is a 35 U.S.C. § 371 national stage application ofPCT/US2016/027303, filed Apr. 13, 2016, and entitled “Nonlinear OpticalMaterial and Methods of Fabrication”, which claims priority to U.S.Patent Application No. 62/146,693, entitled “A Nonlinear OpticalMaterial and Methods of Fabrication,” filed Apr. 13, 2015, thedisclosure of each of which is incorporated by reference in theirentirety herein for all purposes.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

BACKGROUND

Nonlinear optical (NLO) materials may be employed for applicationsincluding optical switching and power limitation as well as imageprocessing and manipulation. Nonlinear optical behavior is the behaviorof light in nonlinear materials where the dielectric polarization has anonlinear response to the electric field of light applied, for example,when the electric field may be of an interatomic strength. In the fieldof nonlinear optical materials, a solid-state laser of a specificwavelength that may be about 1064 nm (infrared), as compared to visiblelight which is from roughly 400 nm (blue) to 700 nm (red). The term‘solid-state laser’ is used, since what is being used to lase is aNd:YAG (neodymium-doped yttrium aluminum garnet—a solid material). Whenthis laser light hits a NLO material, the resulting laser light is halfthe wavelength, i.e. 1064 nm goes in and 532 nm (green) comes out. Withproper optics and a NLO crystal, a 532 nm laser may be fabricated bystarting with a 1064 nm laser. This fabrication is termedsecond-harmonic generation (SHG)—1064 nm/2=532 nm. If another NLOcrystal is disposed in front of the 532 nm light, that radiation wouldbe halved, i.e. 532 nm/2=266 nm, or 1064 nm/4=266 nm. This is termedfourth harmonic generation (FOHG). It is appreciated that the order ofthe harmonic generation is based on the original wavelength of 1064 nm.

BRIEF SUMMARY OF THE DISCLOSURE

In an embodiment, a device comprising: a nonlinear optical (NLO)material according to the formula A_(q)B_(y)C_(z) and having acrystallographic non-centrosymmetric (NCS) structure.

In an embodiment, a method of fabricating polycrystalline non-linearoptical (NLO) materials comprising: heating a vessel containing aplurality of components according to a protocol, wherein the protocolcomprises a plurality of portions; forming, subsequent to completing theprotocol, a polycrystalline material comprising a crystallographicnon-centrosymmetric (NCS) structure having an SHG at 1064 nm from about42 a.u. to about 110 a.u

In an embodiment, a method of fabricating an NLO material comprising:heating a vessel containing a polycrystalline non-linear opticalmaterial according to a protocol, wherein the polycrystalline materialis according to a formula A_(q)B_(y)C_(z), and wherein the materialcomprises crystallographic non-centrosymmetric (NCS) structure; andforming, in response to the heating according to the protocol, aplurality of single crystals from about 0.1 mm to about 10 mm indiameter.

Embodiments described herein comprise a combination of features andcharacteristics intended to address various shortcomings associated withcertain prior devices, compositions, systems, and methods. The variousfeatures and characteristics described above, as well as others, will bereadily apparent to those of ordinary skill in the art upon reading thefollowing detailed description, and by referring to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a ball-and-stick diagram of molecules of BZBP fabricatedaccording to certain embodiments of the present disclosure.

FIGS. 1B-1D are schematic illustrations of components and compounds thatmake up the BZBP fabricated according to certain embodiments of thepresent disclosure.

FIGS. 2A-2D illustrate the second harmonic image generation (SHG)results with respect to particle size for samples of BZBP fabricatedaccording to certain embodiments of the present disclosure in comparisonwith other compounds.

FIG. 3 is a graph of the differential thermal analysis (DTA) results ofsamples of BZBP fabricated according to certain embodiments of thepresent disclosure.

FIG. 4 is a graph of the calculated and experimental results for anx-ray diffraction (XRD) pattern for BZBP fabricated according to certainembodiments of the present disclosure.

FIG. 5 is a photograph of BZBP fabricated according to certainembodiments of the present disclosure.

FIG. 6 illustrates an infrared (IR) spectrum of NLO materials fabricatedaccording to certain embodiments of the present disclosure.

FIG. 7 illustrates the piezoelectric measurement data for samples ofBZBP fabricated according to certain embodiments of the presentdisclosure.

FIG. 8 illustrates polarization measurements for samples of BZBPfabricated according to certain embodiments of the present disclosure.

FIG. 9 illustrates a plot of temperature v. pyroelectric coefficient(P^(T)) and a plot of temperature v. maximum polarization (P) of BZBPfabricated according to certain embodiments of the present disclosure.

FIGS. 10A and 10B illustrate reflectance and absorption of samples ofBZBP fabricated according to certain embodiments of the presentdisclosure.

FIGS. 11A and 11B illustrate flow diagrams of methods of fabricatingsamples of polycrystalline and single crystal BZBP according to certainembodiments of the present disclosure.

DETAILED DESCRIPTION OF THE DISCLOSED EXEMPLARY EMBODIMENTS

The following discussion is directed to various exemplary embodiments.However, one of ordinary skill in the art will understand that theexamples disclosed herein have broad application, and that thediscussion of any embodiment is meant only to be exemplary of thatembodiment, and not intended to suggest that the scope of thedisclosure, including the claims, is limited to that embodiment.

The drawing figures are not necessarily to scale. Certain features andcomponents herein may be shown exaggerated in scale or in somewhatschematic form and some details of conventional elements may not beshown in interest of clarity and conciseness.

In the following discussion and in the claims, the terms “including” and“comprising” are used in an open-ended fashion, and thus should beinterpreted to mean “including, but not limited to . . . .”

Conventional Methods and Materials

Conventionally, there are commercially available materials for lasersthat will go from 1064 mn to 532 nm and from 1064 nm to 266 nm. For thelatter, materials such as β-BaB₂O₄(β-BBO) and CsLiB₆O₁₀ (CLBO) areavailable and used in commercially available lasers. β-BBO and CLBO arethe NLO crystals conventionally employed for 266 nm lasers. For example,a laser at 177.3 nm would be a sixth harmonic generation (SxHG), or1064/6=177.3 nm. The solid-state laser that could work at 177.3 nm canbe employed in photolithography and other advanced technologies.Conventionally, there has been one material that has been shown to laseat 177.3 nm-KBe₂BO₃F₂(KBBF). However, KBBF has both manufacturing andapplication challenges issues. For example, (1) To synthesize KBBF, BeOmust be employed, and BeO is highly toxic and may have restrictions onexperimentation and use; (2) Even though KBBF was discovered in the late1990's, the largest crystal grown to date is 4 mm due to the layeredstructure of the material; and (3) KBBF was discovered overseas andexports of the material have been constrained or halted because of itstechnological applications.

The publication “Design and Synthesis of the Beryllium-FreeDeep-Ultraviolet Nonlinear Optical Material, Ba₃(ZnB₅O₁₀)PO₄,” AdvancedMaterials, October 2015, by Hongwei Yu, Weiguo Zhang, Joshua Young,James M. Rondinelli, and P. Shiv Halasyamani is incorporated byreference in its entirety herein.

Characterization of BZBP Material

The BZBP material fabricated according to certain embodiments of thepresent disclosure may be employed for NLO applications below 200 nm,for example, at 177.3 nm. The BZBP material may be fabricated as apolycrystalline material or as an at least one single crystal (or aplurality of single crystals). The following attributes may be desirablefor deep-UV NLO applications: (i) crystallographic non-centrosymmetric(NCS) structure, (ii) large transparency window, i.e. a wide band gap,(iii) large second-harmonic generating (SHG) coefficient, (iv) moderatebirefringence, (v) chemically stable with a large laser damagethreshold, and (vi) easy (repeatable, cost-effective) growth of largevolume (cm³) single crystals. As such, those properties andcharacteristics are measured and discussed herein.

Definitions

A “laser damage threshold” is a term used herein to define a peakfluency of laser irradiation at which irreversible changes in amaterial's structure may occur. This laser damage threshold may bedefined as the highest quantity of laser radiation that a material mayabsorb before there are changes to the material's optical properties.This may also be defined by the ISO standards 21254-1, 2, 3, and 4definitions as the highest quantity of laser radiation incident upon theoptical component for which the extrapolated probability of damage iszero where the quantity of laser radiation may be expressed as powerdensity, linear power density or energy density.

“Anisotropy” is the term used to define properties/characteristics ofmaterial that may vary depending upon the direction in which theproperties/characteristics are observed/measured.

“Birefringence,” which may be referred to as “double refraction,” is anoptical material property where a light passing through a crystal issplit into two unequal wavelengths, which then each pass through thecrystal at different respective speeds. Birefringence is exhibited inoptically anisotropic crystals.

“Non-centrosymmetric” is a term used to describe the symmetry (or lackthereof) of certain crystal structures. Non-centrosymmetric materialsare materials where point groups lack an inversion center, in contrastto centrosymmetric structures and materials which comprise a unit cell(e.g., face-centered-cubic, “fcc”) that has a center of symmetry at, forexample, (0,0,0). In this example, the inversion centers may be observedat atom sites such as the atom at (0, 0, ½), which would invert to theatom at (0, 0, −½), and the atom at (½,½, 0) inverts to (−½, −½, 0).While an fcc structure comprises an inversion center at every atom, astructure may be characterized as centrosymmetric if it comprises atleast one inversion center, and may be characterized asnon-centrosymmetric if it does not comprise any inversion centers.

“Band gap” is the characteristic of a material, such as an opticalmaterial, that is associated with the minimum energy needed to move anelectron from a bound state (valence band) into a free state (conductionband). Varying energy band structures in semiconductors are associatedwith the electrical (including thermoelectric) properties exhibited bythese semiconductors.

Overview

Nonlinear optical (NLO) materials are of intense interest owing to theirability to control and manipulate light for the generation of coherentradiation at a variety of difficult to access wavelengths. They haveefficiently expanded the spectral ranges of solid state lasers fromultraviolet (UV) to infrared (IR). Accessing directly thedeep-ultraviolet (DUV) region (L<200 nm), however, is especiallychallenging, yet desirable for a number of advanced opticaltechnologies, including photolithography for microelectronics andattosecond pulse generation for electron dynamic studies in matter. Assuch, the design and synthesis of a chemically benign Be-freeboratephosphate, Ba₃(ZnB₅O₁₀)PO₄ (“BZBP”), which exhibits a widetransparency range with second-harmonic-generating properties comparableto KBe₂BO₃F₂ (“KBBF”), a material currently employed to generatecoherent DUV radiation directly using direct second harmonic generation(SHG). BZBP is air stable to 1000° C. and melts congruently, allowingfor facile growth of large crystals and making it ideally suited for NLOapplications in the DUV.

Synthesis of BZBP

In an embodiment, polycrystalline Ba₃ZnB₅PO₁₄ was synthesized bysolid-state methods. The stoichiometric amounts of BaCO₃ (FisherScientific, 99%), ZnO (Assay, 99.0%), H₃BO₃ (Alfa Aesar, 99.0%), andNH₄H₂PO₄ (Alfa Aesar, 98.0%) were ground thoroughly, packed tightly in aplatinum crucible, and heated to 400° C. for 20 h to decompose ammoniumdihydrogen phosphate and borates, and then the temperature was raised to840° C. held for 72 h with several intermittent grindings, thetemperature was then reduced to room temperature. In this manner, pureBa₃ZnB₅PO₁₄ can be obtained. As discussed herein, an “intermittentgrinding” refers to a process by which the components are removed fromthe heating vessel, ground, and in some embodiments ground, sifted toremove a predetermined particle size or range, ground again, andre-sifted for a predetermined number of cycles.

There may be one or more intermittent grinding processes during the heattreat process, and the heating time, temperature, number of intermittentgrindings, time at temperature (and/or time ramping up/down and range ofthe ramp up/down) may be collectively referred to as a “recipe,” a“program,” or a “protocol” interchangeably herein, and may be referredto in portions or segments in order to discuss the method of BZBP aswell as the characterization of the fabricated material. In anembodiment, a “portion” of the protocol comprises a single temperatureor a temperature range within which the BZBP is held (in the vessel) fora predetermined period of time before being held at a differenttemperature or temperature range.

In an alternate embodiment, a single crystal of Ba₃ZnB₅PO₁₄ was grown byre-crystallizing the pure polycrystalline samples fabricated accordingto certain embodiments herein. In an embodiment, the Ba₃ZnB₅PO₁₄polycrystalline sample was melted at 940° C. for about 20 h, and then itwas cooled down to 700° C. at a rate of 2° C./h. Finally, it wasquenched to room temperature. Millimeter size and colorless singlecrystals of Ba₃ZnB₅PO₁₄ were obtained by this process. In an embodiment,the size of the single crystals fabricated e may be from about 0.1 mm toabout 1.5 mm in maximum diameter, and may be cube or rectangular-shaped.In an embodiment, the material fabricated is free from, and thus doesnot comprise, beryllium.

In another embodiment, pure and polycrystalline BZBP was synthesizedthrough solid-state techniques as discussed herein by combiningstoichiometric amounts of BaCO₃, ZnO, H₃BO₃, and NH₄H₂PO₄ in a Ptcrucible and heating the crucible in air. The phase purity was confirmedby powder X-ray diffraction as discussed herein. Single crystals of BZBPwere grown by a top-seeded solution growth method. A H₃BO₃—ZnO fluxsystem was used for the crystal growth. The mixture was placed in a Ptcrucible and melted at 980° C. This temperature was held for 15 h afterwhich a Pt wire was dipped into the clear melt. Small crystals nucleatedon the Pt wire and were used as seed crystals that were dipped into themelt as discussed herein in order to seed larger single crystals. Usingthe seed crystals, BZBP crystals of about 9×7×3 mm³ were grown andindexed (FIG. 4). Layering of the single crystal is not observed inBZBP, which overcomes the layering-growth habit along the c-axisreported for KBBF, and may be attributable to the ZnB₅O₁₀ units that arelinked in three dimensions (see FIGS. 1B-1D below).

While certain embodiments are discussed herein, the BZBP may befabricated according to a formula of A_(q)B_(y)C_(z), where A comprisesat least one of an alkali metal or an alkaline earth metal, B comprisesat least two of boron (B), carbon (C), or a transition metal, andwherein D comprises at least one of oxygen (O), phosphorous (P), andfluorine (F). In an embodiment, q, x, and y are each from about 1 toabout 10, and wherein z is from about 1 to about 20. In someembodiments, the material is according to a composition Ba₃ZnB₅PO₁₄.

Table 1 provides exemplary data for BZBP material fabricated accordingto certain embodiments of the present disclosure, which crystallized inthe noncentrosymmetric orthorhombic polar space group Pmn2₁.

TABLE 1 Empirical formula BZBP Temperature 296 (2) K Wavelength 0.71073Formula weight 786.41 Crystal system Orthorhombic Space group Pmn2₁ Unitcell dimensions a = 10.399 (11) Å b = 7.064 (7) Å c = 8.204 (8) Å Z 2Volume (Å³) 602.6 (11) Calculated density (Mg/m³) 4.334 Absorptioncoefficient (/mm) 11.851 Reflections collected/unique 3479/1352 [R(int)= 0.0343] Completeness to theta (27.48°) 100.0% Goodness-of-fit on F²1.037 Final R indices [I > 2sigma(I)]^([a]) R1 = 0.0219, wR2 = 0.0426Flack factor −0.01 (3) Extinction coefficient 0.0067 (3) Largest diff.peak and hole (e · Å⁻³) 1.089 and −0.857

It is noted that [a] is used in Table 1 to indicated thatR₁=Σ∥F_(o)|−|F_(c)∥/Σ∥F_(o)| and wR₂=[Σw(F_(o) ²−F_(c) ²)²/Σw F_(o)⁴]^(1/2) for F_(o) ²>2σ(F_(o) ²).

Table 2 illustrates the atomic coordinates (×10⁴) and equivalentisotropic displacement parameters (Å²×10³) for Ba₃(ZnB₅O₁₀)PO₄. U_(eq)is defined as one-third of the trace of the orthogonalized U_(ij)tensor. In the asymmetric unit, there are two unique Ba atoms, oneunique Zn atom, one unique P atom, three unique B atoms, and nine Oatoms. The B atoms exhibit two types of coordination environments—BO 3triangles and BO 4 tetrahedra. The B—O bond distances range from1.330(8) to 1.396(9) Å and 1.463(7) to 1.491(7) Å, respectively. The Pand Zn atoms are coordinated by four O atoms to form PO₄ and ZnO₄tetrahedra. The P—O and Zn—O bond distances range from 1.539(4) to1.545(6) Å and 1.941(7) to 2.065(6) Å, respectively.

TABLE 2 Atom x y z U_(eq) BVS Ba(1) 2298 (1) 4348 (1) 9390 (1) 12 (1)1.95 Ba(2) 0 294 (1) 7253 (1) 10 (1) 2.16 Zn(1) 5000 7603 (2) 8330 (1)10 (1) 1.89 P(1) 0 5663 (3) 6611 (3) 11 (1) 4.91 B(1) 2623 (6) 9471 (9)9259 (12) 8 (1) 3.00 B(2) 3775 (6) 11026 (10) 6740 (8) 7 (1) 2.99 B(3)5000 4107 (15) 6609 (13) 10 (2) 2.97 O(1) 1223 (4) 6799 (6) 7012 (6) 13(1) 1.99 O(2) 5000 10294 (8) 7349 (10) 9 (1) 1.94 O(3) 1163 (4) 6879 (6)11578 (5) 10 (1) 2.09 O(4) 0 3867 (10) 7687 (7) 15 (2) 2.21 O(5) 50005984 (9) 6418 (8) 9 (1) 1.99 O(6) 0 5202 (9) 4776 (7) 15 (1) 1.87 O(7)3455 (4) 8111 (6) 9640 (5) 15 (1) 1.97 O(8) 2720 (4) 693 (6) 7938 (5) 9(1) 2.07 O(9) 1525 (4) −116 (6) 10170 (5) 11 (1) 1.89

Table 3 illustrates the selected bond distances (Å) and angles (deg) forBa₃(ZnB₅O₁₀)PO₄. The P and Zn atoms are coordinated by four O atoms toform PO₄ and ZnO₄ tetrahedra. The P—O and Zn—O bond distances range from1.539(4) to 1.545(6) Å and 1.941(7) to 2.065(6) Å, respectively. The Baatoms are coordinated by nine O atoms with Ba—O bond lengths rangingfrom 2.549(7) to 2.938(5) Å. These bond lengths are consistent withthose known for oxides containing Ba, including known borophosphates.

TABLE 3 Ba(1)-O(1)#1 2.766 (5) O(1)#1-Ba(1)-O(9) 72.92 (12) Ba(1)-O(4)2.788 (4) O(4)-Ba(1)-O(9) 76.91 (15) Ba(1)-O(3) 2.795 (5)O(3)-Ba(1)-O(9) 112.47 (13) Ba(1)-O(1) 2.838 (5) O(1)-Ba(1)-O(9) 128.13(13) Ba(1)-O(6)#1 2.846 (3) O(6)#1-Ba(1)-O(9) 108.92 (14) Ba(1)-O(8)2.877 (5) O(8)-Ba(1)-O(9) 42.59 (12) Ba(1)-O(5)#1 2.921 (4)O(5)#1-Ba(1)-O(9) 67.39 (15) Ba(1)-O(7) 2.925 (5) O(7)-Ba(1)-O(9) 161.84(11) Ba(1)-O(3)#2 2.938 (5) O(3)#2-Ba(1)-O(9) 90.18 (12) Ba(2)-O(4)2.549 (7) O(4)-Ba(2)-O(1)#4 152.63 (9) Ba(2)-O(1)#3 2.784 (5)O(1)#3-Ba(2)-O(1)#4 54.34 (18) Ba(2)-O(1)#4 2.784 (5) O(4)-Ba(2)-O(9)89.07 (14) Ba(2)-O(9) 2.885 (5) O(1)#3-Ba(2)-O(9) 102.75 (14)Ba(2)-O(9)#5 2.885 (5) O(1)#4-Ba(2)-O(9) 73.67 (13) Ba(2)-O(8)#5 2.897(5) O(4)-Ba(2)-O(9)#5 89.07 (14) Ba(2)-O(8) 2.897 (5)O(1)#3-Ba(2)-O(9)#5 73.67 (14) Ba(2)-O(7)#6 2.906 (5)O(1)#4-Ba(2)-O(9)#5 102.75 (14) Ba(2)-O(7)#2 2.906 (5) O(9)-Ba(2)-O(9)#566.66 (17) Zn(1)-O(5) 1.941 (7) O(4)-Ba(2)-O(8)#5 82.91 (8) Zn(1)-O(7)1.966 (4) O(1)#3-Ba(2)-O(8)#5 69.78 (13) Zn(1)-O(7)#7 1.966 (4)O(1)#4-Ba(2)-O(8)#5 123.08 (12) Zn(1)-O(2) 2.065 (6) O(9)-Ba(2)-O(8)#5112.67 (13) P(1)-O(6) 1.540 (6) O(9)#5-Ba(2)-O(8)#5 46.57 (12)P(1)-O(1)#5 1.539 (4) O(4)-Ba(2)-O(8) 82.91 (8) P(1)-O(1) 1.539 (4)O(1)#3-Ba(2)-O(8) 123.08 (12) P(1)-O(4) 1.545 (6) O(1)#4-Ba(2)-O(8)69.78 (13) B(1)-O(7) 1.330 (8) O(9)-Ba(2)-O(8) 46.57 (12) B(1)-O(8)#81.390 (9) O(9)#5-Ba(2)-O(8) 112.67 (13) B(1)-O(9)#8 1.396 (9)O(8)#5-Ba(2)-O(8) 154.94 (17) B(2)-O(2) 1.463 (7) O(4)-Ba(2)-O(7)#673.67 (14) B(2)-O(9)#2 1.473 (8) O(1)#3-Ba(2)-O(7)#6 92.24 (14)B(2)-O(3)#9 1.487 (8) O(1)#4-Ba(2)-O(7)#6 122.96 (14) B(2)-O(8)#8 1.491(7) O(9)-Ba(2)-O(7)#6 162.65 (13) B(3)-O(5) 1.335 (12)O(9)#5-Ba(2)-O(7)#6 110.30 (14) B(3)-O(3)#2 1.396 (7)O(8)#5-Ba(2)-O(7)#6 64.25 (13) B(3)-O(3)#10 1.396 (7) O(8)-Ba(2)-O(7)#6130.17 (12) O(1)#1-Ba(1)-O(4) 146.18 (15) O(4)-Ba(2)-O(7)#2 73.67 (14)O(1)#1-Ba(1)-O(3) 85.56 (14) O(1)#3-Ba(2)-O(7)#2 122.96 (14)O(4)-Ba(1)-O(3) 92.19 (17) O(1)#4-Ba(2)-O(7)#2 92.24 (14)O(1)#1-Ba(1)-O(1) 158.80 (6) O(9)-Ba(2)-O(7)#2 110.30 (14)O(4)-Ba(1)-O(1) 52.58 (16) O(9)#5-Ba(2)-O(7)#2 162.65 (13)O(3)-Ba(1)-O(1) 83.39 (13) O(8)#5-Ba(2)-O(7)#2 130.17 (12)O(1)#1-Ba(1)-O(6)#1 52.90 (15) O(8)-Ba(2)-O(7)#2 64.25 (13)O(4)-Ba(1)-O(6)#1 156.27 (16) O(7)#6-Ba(2)-O(7)#2 67.13 (18)O(3)-Ba(1)-O(6)#1 105.87 (15) O(5)-Zn(1)-O(7) 123.31 (14)O(1)-Ba(1)-O(6)#1 113.40 (15) O(5)-Zn(1)-O(7)#7 123.31 (14)O(1)#1-Ba(1)-O(8) 88.54 (13) O(7)-Zn(1)-O(7)#7 109.6 (3) O(4)-Ba(1)-O(8)79.29 (16) O(5)-Zn(1)-O(2) 103.1 (3) O(3)-Ba(1)-O(8) 154.77 (12)O(7)-Zn(1)-O(2) 92.59 (18) O(1)-Ba(1)-O(8) 108.84 (14) O(7)#7-Zn(1)-O(2)92.59 (18) O(6)#1-Ba(1)-O(8) 89.76 (15) O(5)-Zn(1)-O(6)#1 84.8 (2)O(1)#1-Ba(1)-O(5)#1 89.35 (15) O(7)-Zn(1)-O(6)#1 82.86 (15)O(4)-Ba(1)-O(5)#1 64.84 (16) O(7)#7-Zn(1)-O(6)#1 82.86 (15)O(3)-Ba(1)-O(5)#1 48.73 (16) O(2)-Zn(1)-O(6)#1 172.0 (3)O(1)-Ba(1)-O(5)#1 96.80 (15) O(6)-P(1)-O(1)#5 108.6 (2)O(6)#1-Ba(1)-(5)#1 138.87 (16) O(6)-P(1)-O(1) 108.6 (2)O(8)-Ba(1)-O(5)#1 106.78 (15) O(1)#5-P(1)-O(1) 111.4 (4)O(1)#1-Ba(1)-O(7) 89.00 (14) O(6)-P(1)-O(4) 112.6 (4) O(4)-Ba(1)-O(7)119.88 (16) O(1)#5-P(1)-O(4) 107.8 (2) O(3)-Ba(1)-O(7) 63.06 (13)O(1)-P(1)-O(4) 107.8 (2) O(1)-Ba(1)-O(7) 69.86 (14) O(7)-B(1)-O(8)#8125.8 (6) O(6)#1-Ba(1)-O(7) 58.95 (15) O(7)-B(1)-O(9)#8 123.9 (7)O(8)-Ba(1)-O(7) 141.42 (12) O(8)#8-B(1)-O(9)#8 110.3 (5)O(5)#1-Ba(1)-O(7) 111.68 (15) O(2)-B(2)-O(9)#2 109.2 (5)O(1)#1-Ba(1)-O(3)#2 102.78 (12) O(2)-B(2)-O(3)#9 110.1 (5)O(4)-Ba(1)-O(3)#2 92.14 (16) O(9)#2-B(2)-O(3)#9 111.4 (5)O(3)-Ba(1)-O(3)#2 157.33 (7) O(2)-B(2)-O(8)#8 111.1 (5)O(1)-Ba(1)-O(3)#2 81.65 (14) O(9)#2-B(2)-O(8)#8 110.6 (5)O(6)#1-Ba(1)-O(3)#2 65.33 (15) O(3)#9-B(2)-O(8)#8 104.4 (5)O(8)-Ba(1)-O(3)#2 47.71 (11) O(5)-B(3)-O(3)#2 119.6 (4)O(5)#1-Ba(1)-O(3)#2 150.35 (15) O(5)-B(3)-O(3)#10 119.6 (4)O(7)-Ba(1)-O(3)#2 95.69 (12) O(3)#2-B(3)-O(3)#10 120.1 (9)

The symmetry transformations used to generate equivalent atoms in Table3 are indicated below:

#1 −x+½,−y+1,z+½

#2 −x+½,−y+1,z−½

#3 −x,y−1,z

#4 x,y−1,z

#5 −x,y,z

#6 x−½,−y+1,z−½

#7 −x+1,y,z

#8 x,y+,z

#9 −x+½,−y+2,z−½

#10 x+½,−y+1,z−½

#11 −x+½,−y+2,z+½

Discussion of Fabrication, Characterization, and Application of BZBP

Referring to FIG. 1A, a plurality of molecules are shown for the BZBPmaterial fabricated according to certain embodiments of the presentdisclosure. In particular in FIG. 1A, the arrangement of molecules ofBZBP 100 is illustrated, as is a single molecule 102 of BZBP, therectangular outline indicates the single molecule 102. In FIG. 1A, 104indicates the barium (Ba) molecules, 106 indicates the zinc (Zn)molecules, 108 indicates the boron (B) molecules, 110 indicates thephosphorous (P) molecules, and 112 indicates the oxygen (O) molecules.

In an embodiment, as shown in FIG. 1B, the basic building unit of BZBPis a three six-membered ring [ZnB₅O₁₀] group composed of three [BO₃]triangles, two [BO₄] tetrahedra, and one [ZnO₄] tetrahedron that arecornershared through oxygen atoms. The arrow in FIG. 1B indicates therelationship of FIG. 1B to FIG. 1C in that FIG. 1C illustrates a[ZnB₅O₁₀] ∞ framework. As shown in FIG. 1C, the adjacent [ZnB₅O₁₀]building units share corners to create a [ZnB₅O₁₀]∞ framework (FIG. 1C).The Ba atoms and the isolated PO₄ tetrahedra fill the spaces of the[ZnB₅O₁₀] ∞ framework (FIG. 1D). As such, these crystal structuresconfirm that BZBP is a zincoborate-phosphate.

FIGS. 2A-2D illustrate the second harmonic image generation (SHG)results with respect to particle size for BZBP fabricated according tocertain embodiments of the present disclosure in comparison to otheroptical materials. Turning to FIGS. 2A and 2B, the second harmonic imagegeneration (SHG) results with respect to particle size are illustratedfor BBO (the conventional material) and BZBP (the material fabricatedherein). SHG may also be referred to as “frequency doubling” and is theterm used to refer to a nonlinear optical process where new photons aregenerated when photons with the same frequency interact with a nonlinearmaterial, and the new photons generated have twice the energy of theparent photons (and consequently half the wavelength and twice thefrequency). The SHG phenomenon is only found in non-centrosymmetricmaterials, such as the BZBP discussed herein.

FIG. 2A illustrates the SHG data at a wavelength of 532 nm and FIG. 2Billustrates the SHG data at a wavelength of 1064 nm. Both FIGS. 2A and2B confirm that the BZBP material exhibits active SHG behavior at leastat the wavelengths of 532 nm and 1064 nm. For example, in FIG. 2A at 532nm, the BZBP material exhibits an SHG coefficient from about 20 a.u. toabout 30 a.u. between a particle size of about 35 μm to about 130 μm.This “particle size” refers to the final particle size after anygrinding prior to heat treat as well as any grinding done during theheating process. This is in comparison to the BBO results which werefrom about 68 a.u. to about 80 a.u. over about the same particle sizerange.

FIG. 2B shows that, at 1064 nm, the BZBP material exhibits an SHGcoefficient from about 35 a.u. to about 70 a.u. between a particle sizeof about 35 m to about 120 m, as compared to the BBO material over thesame particle size range which exhibited a range from about 130 a.u. toabout 135 a.u.

FIG. 2C illustrates particle size v. SHG for BZBP fabricated accordingto certain embodiments of the present disclosure as compared toPotassium Dihydrogen Phosphate (KDP). FIG. 2D illustrates particle sizev. SHG for BZBP fabricated according to certain embodiments of thepresent disclosure as compared to β-BBO. The frequency doublingcapabilities of polar BZBP. The SHG efficiencies as a function ofparticle size, as shown in FIGS. 2C and 2D, indicate that BZBP has SHGefficiencies of approximately 4×KDP and 0.5×β-BBO at 532 and 266 nm,respectively, in the 45-63 m particle range. Furthermore, BZBP is type-1phase-matchable at both wavelengths.

Referring now to FIG. 3, the differential thermal analysis (DTA) ofsamples of BZBP fabricated according to certain embodiments of thepresent disclosure illustrates the reaction of the BZBP material fromabout 200° C. to about 1200° C. In particular, FIG. 3 illustrates thebehavior of the material through a heating cycle and a cooling cycle, asindicated. Temperature stability was observed above about 900° C., andthe TG data illustrates that there was virtually no weight loss as aresult of the increasing temperature. There is only one endothermic(exothermic) peak on the heating (cooling) curve at 937° C. (827° C.),indicating BZBP melts congruently. In addition, in this embodiment,there was no weight loss observed up to 1000° C.

Referring now to FIG. 4, an XRD pattern was calculated for thepure-phase of BZBP, and compared to the results of the XRD pattern forsamples of BZBP fabricated according to certain embodiments of thepresent disclosure. The calculated and experimental x-ray diffractionpatterns match, which indicates that the samples fabricated are purematerials.

FIG. 5 is a photograph of BZBP fabricated according to certainembodiments of the present disclosure. FIG. 5 illustrates that thelargest outer diameter of these crystals may be less than 2 mm.

FIG. 6 illustrates an infrared (IR) spectrum of NLO materials fabricatedaccording to certain embodiments of the present disclosure. The IRspectrum was recorded with a Bruker Tensor 37 FTIR spectrometer in the400-4000 cm⁻¹ wave number range using KBr pellets (Figure S3). The mainIR absorption region between 1458 and 507 cm⁻¹ reveals severalabsorption bands on account of stretching and bending vibrations of theB—O and P—O groups, which are similar to those of otherborate-phosphates.

FIG. 7 illustrates the piezoelectric measurement data for samples ofBZBP fabricated according to certain embodiments of the presentdisclosure.

FIG. 8 illustrates polarization measurements for samples of BZBPfabricated according to certain embodiments of the present disclosure.The BZBP sample was pressed into pellets (˜12 mm diameter, ˜1 mmthickness) and sintered at 850° C. for 10 h. Silver paste was applied toboth sides as electrodes. The polarization was measured on a RadiantTechnologies RT66A Ferroelectric Test system with a TREK high voltageamplifier between 30 and 230° C. in 10° C. increments with a 15 kV/cmelectric field at 500 Hz. To determine any ferroelectric behavior, thepolarization loop was measured at room temperature under a 15 kV/cmstatic electric field with the frequency ranging from 50 to 500 Hz. Asshown in FIG. 8, the polarization versus electric field plots at 15kV/cm electric field vary with the different frequencies. Note thatthere is no hysteresis, indicating that the material is notferroelectric; that is, the polarization is not reversible.

FIG. 9 illustrates a plot of temperature v. pyroelectric coefficient(P^(T)) and a plot of temperature v. maximum polarization (P) of BZBPfabricated according to certain embodiments of the present disclosure.

FIG. 10A shows the UV-vis-IR diffuse-reflectance spectrum forpolycrystalline BZBP. Polycrystalline BZBP has a largetransmission, >90%, from 230 to 2500 nm, with a short UV cutoff edgebelow 200 nm as determined from the UV-vis-IR diffuse-reflectancespectrum. The reflectance at 200 nm is nearly 80%, indicating BZBP istransparent well below 200 nm. In order to investigate the DUVabsorption, additional measurements were performed on a single crystalof BZBP on a McPherson VUVas2000 spectrophotometer from 120 to 350 nmand are illustrated in FIG. 10B. FIG. 10B indicates that the absorptionedge is 180 nm, confirming that the optical transparency of BZBP isadvantageous for frequency generation in the DUV. The inset in FIG. 10Bshows a single crystal with a thickness of about 1 mm that was cut froma crystal of BZBP fabricated according to certain embodiments of thepresent disclosure.

Turning to FIG. 11A, a method 1100 may be used to fabricatepolycrystalline BZBP. At block 1102 of the method 1100, stoichiometricamounts of a plurality of components are ground to a predetermined meanparticle size or range of particle sizes. In an embodiment, theplurality of components comprises BaCO₃, ZnO, H₃BO₃, and NH₄H₂PO₄ wereground thoroughly at block 1102 and packed tightly in a vessel such as aplatinum crucible at block 1104. At block 1106, the packed groundmaterial may be heated one or more times and may be held at differenttemperatures for varying predetermined periods of time. Heating thematerial and then holding the heated material at a temperature isdescribed herein as a cycle. One or more such cycles, when performed ina sequence, may be part of a protocol. In an embodiment, the vessel (andtherefore the components in the vessel) may be heated according to aprotocol at block 1106 that may comprise a first portion 1106A, a secondportion 1106B, and a third portion 1106C. In different embodiments, theprotocol executed at block 1106 may comprise greater or fewer portions,which may comprise various degrees and times of heating as well asvarious quench programs. In an embodiment, during the first portion1106A, the vessel is heated from a first temperature to a second duringa first duration of time, during which the particle size of thecomponents may be further reduced during at least one grinding cycle. Ina subsequent second portion 1106B, the vessel is heated from a thirdtemperature to a fourth during a second duration of time, during whichthe particle size of the components may be further reduced during atleast one grinding cycle. At least one of the third or fourthtemperatures in the second portion 1106B may be greater than the secondtemperature in the first portion 1106B. In some embodiments, the secondduration of time at block 1106B may be longer than the first duration oftime in block 1106A. In an embodiment, at block 1106C, a quench mayoccur.

In an embodiment, the vessel may be heated at block 1106 using aprotocol comprising holding the ground components in a first portion1106A at about 400° C. during a first protocol portion for about 20 h todecompose ammonium dihydrogen phosphate and borates. In this exampleprotocol, the temperature was raised to 840° C. and held for 72 h duringa second protocol portion at block 1106B. In some embodiments, thecomponents may be further ground one or more times at block 1106A and/or1106B during one, some, or all portions of the protocol. In the exampleprotocol, the temperature was reduced to room temperature after thesecond portion at 840° C. At block 1108, subsequent to cooling, thepure, polycrystalline Ba₃ZnB₅PO₁₄ was obtained.

FIG. 11B illustrates an alternate method embodiment 1200 which may startat block 1108 in FIG. 11A. At block 1108 in FIG. 11A, thepolycrystalline Ba₃ZnB₅PO₁₄ was fabricated. In the method 1200, a singlecrystal of Ba₃ZnB₅PO₁₄ was grown by re-crystallizing the purepolycrystalline samples. That is, at block 1110, the Ba₃ZnB₅PO₁₄polycrystalline sample was melted using a protocol comprising at leasttwo portions. In an embodiment, the vessel (and therefore the componentsin the vessel) may be heated according to a protocol at block 1110 thatmay comprise a first portion 1110A, a second portion 1110B, and a thirdportion 1110C. In different embodiments, the protocol executed at block1110 may comprise greater or fewer portions, which may comprise variousdegrees and times of heating as well as various quench programs. In anembodiment, during the first portion 1110A, the vessel is heated from afirst temperature to a second during a first duration of time, duringwhich the particle size of the components may be further reduced duringat least one grinding cycle. In a subsequent second portion 1110B, thevessel is heated from a third temperature to a fourth during a secondduration of time, during which the particle size of the components maybe further reduced during at least one grinding cycle. At least one ofthe third or fourth temperatures in the second portion 1110B may be lessthan the second temperature in the first portion 1110B. In someembodiments, the second duration of time at block 1110B may be longerthan the first duration of time in block 1110A. In an embodiment, atblock 1110C, a quench may occur and a plurality of single crystal may beformed at block 1112.

In one example, the polycrystalline BZBP is held during a first portionof a protocol at block 1110A at about 940° C. for about 20 h, and thenit was cooled down during a second portion of the protocol to about 700°C. at a rate of 2° C./h at block 1110B. Finally, in a third portion ofthe protocol at block 1110C, the polycrystalline BZBP was quenched toroom temperature. At block 1112, subsequent to quenching, millimetersize, pure, and colorless crystals of Ba₃ZnB₅PO₁₄ were obtained. Invarious embodiments, these single crystals may range in maximum diameterfrom 0.5 mm to about 10 mm, and may be used to seed the growth ofadditional single crystals using a top-seeded-solution growth method.

Exemplary embodiments are disclosed and variations, combinations, and/ormodifications of the embodiment(s) and/or features of the embodiment(s)made by a person having ordinary skill in the art are within the scopeof the disclosure. Alternative embodiments that result from combining,integrating, and/or omitting features of the embodiment(s) are alsowithin the scope of the disclosure. Where numerical ranges orlimitations are expressly stated, such express ranges or limitationsshould be understood to include iterative ranges or limitations of likemagnitude falling within the expressly stated ranges or limitations(e.g., from about 1 to about 10 includes, 2, 3, 4, etc.; greater than0.10 includes 0.11, 0.12, 0.13, etc.). For example, whenever a numericalrange with a lower limit, R_(l), and an upper limit, R_(u), isdisclosed, any number falling within the range is specificallydisclosed. In particular, the following numbers within the range arespecifically disclosed: R=R_(l)+k*(R_(u)−R_(l)), wherein k is a variableranging from 1 percent to 100 percent with a 1 percent increment, i.e.,k is 1 percent, 2 percent, 3 percent, 4 percent, 5 percent, . . . , 50percent, 51 percent, 52 percent, . . . , 95 percent, 96 percent, 97percent, 98 percent, 99 percent, or 100 percent. Moreover, any numericalrange defined by two R numbers as defined in the above is alsospecifically disclosed. Use of broader terms such as “comprises,”“includes,” and “having” should be understood to provide support fornarrower terms such as “consisting of,” “consisting essentially of,” and“comprised substantially of.” Accordingly, the scope of protection isnot limited by the description set out above but is defined by theclaims that follow, that scope including all equivalents of the subjectmatter of the claims.

While exemplary embodiments of the invention have been shown anddescribed, modifications thereof can be made by one skilled in the artwithout departing from the scope or teachings herein. The embodimentsdescribed herein are exemplary only and are not limiting. Manyvariations and modifications of the compositions, systems, apparatus,and processes described herein are possible and are within the scope ofthe invention. Accordingly, the scope of protection is not limited tothe embodiments described herein, but is only limited by the claims thatfollow, the scope of which shall include all equivalents of the subjectmatter of the claims. Unless expressly stated otherwise, the steps in amethod claim may be performed in any order and with any suitablecombination of materials and processing conditions.

What is claimed is:
 1. A method of fabricating a polycrystallinenon-linear optical (NLO) material, the method comprising: heating avessel containing a plurality of components according to a protocol,wherein the protocol comprises a plurality of portions; forming,subsequent to completing the protocol, a polycrystalline NLO materialcomprising a crystallographic non-centrosymmetric (NCS) structure havingan SHG at 1064 nm from about 42 a.u. to about 110 a.u.
 2. The method ofclaim 1 further comprising grinding the plurality of components one ofprior to heating the vessel or during the protocol, wherein a particlesize of the NLO material is from about 30 μm to about 130 μm.
 3. Themethod of claim 1, wherein a first portion of the protocol comprisesheating the vessel from a first temperature to a second temperature fora first period of time, and a second portion of the protocol comprisesheating the vessel from a third temperature to a fourth temperature fora second period time, wherein the third temperature is higher than thesecond temperature, and wherein the second period of time is greaterthan the first.
 4. The method of claim 3 further comprising grinding,during the second portion, the plurality of components, wherein grindingthe plurality of components comprises further reducing the particle sizeof at least some of the plurality of components at least once during thesecond portion of the protocol.
 5. The method of claim 3 furthercomprising reducing the temperature of the vessel to about roomtemperature.
 6. The method of claim 1, wherein a first portion of theprotocol comprises heating the vessel from about 200° C. to about 600°C. for from about 15 hours to about 20 hours.
 7. The method of claim 6,wherein a second portion of the protocol comprises heating the vesselfrom about 700° C. to about 1000° C. for from about 48 hours to about 96hours.
 8. The method of claim 1, wherein a first portion of the protocolcomprises holding the vessel from about 800° C. to about 1100° C. forfrom about 15 hours to about 25 hours.
 9. The method of claim 8, whereina second portion of the protocol comprises cooling the vessel to below700° C. at a rate from about 0.5° C./h and 3° C./h.
 10. The method ofclaim 9, wherein a third portion of the protocol comprises quenching thevessel to about room temperature.
 11. The method of claim 1, furthercomprising grinding, during a first portion of the protocol, theplurality of components, wherein grinding the plurality of componentscomprises further reducing a particle size of at least some of theplurality of components at least once during the first portion of theprotocol.
 12. The method of claim 1, wherein the polycrystalline NLOmaterial comprises a pure-phase material.
 13. The method of claim 1,wherein the plurality of components are according to a formula ofBa₃ZnB₅PO₁₄.
 14. The method of claim 1, wherein the polycrystalline NLOmaterial is a boratephosphate.
 15. The method of claim 1, wherein thepolycrystalline NLO material is according to a formula AqByCz.
 16. Themethod of claim 15, wherein A comprises an alkali metal or an alkalineearth metal.
 17. The method of claim 15, wherein B comprises at leasttwo of boron (B), carbon (C), or a transition metal.
 18. The method ofclaim 15, wherein C comprises at least one of oxygen (O), phosphorous(P), or fluorine (F).
 19. The method of claim 15, wherein q and y areeach from about 1 to about
 10. 20. The method of claim 15, wherein z isfrom about 1 to about 20.